This invention relates to an improved closure diaphragm for offshore platforms used in well drilling and production.
Offshore platforms are generally fabricated in a harbor or on a shore location and are then towed to a marine site where they are tipped on end and lowered into position with the platform resting on the ocean floor. The platform legs are hollow structures having open ends so that pilings can be driven downwardly through the legs into the subterranean formations below the ocean floor to anchor the platform in position.
It is desirable during platform setting operations to utilize the platform legs and/or pile sleeves for buoyancy to assist in the setting operations. It is also desirable to exclude foreign material from the platform leg and/or pile sleeve during platform setting operations to prevent the annulus between the piling and the platform leg and/or pile sleeve from becoming contaminated with foreign material which would prevent the filling of the annulus with cement or grout. Therefore, a closure structure which is easily severable when the piling is driven through the platform leg and/or pile sleeve is used to seal the end of the platform leg and/or pile sleeve during setting of the platform.
Typical prior art closure structures, generally referred to as closures or diaphragms, utilized to seal the end of a platform leg and/or pile sleeve of an offshore platform, are illustrated in U.S. Pat. Nos. 3,533,241, 4,024,723, 4,178,112, 4,220,422 and 4,230,424. While these closures are generally satisfactory, all utilize layers or plies of reinforcing material comprised of unitary pieces of fabric to reinforce the closure.